Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase that participates in cell cycle control, signal transduction and whose activity is altered during viral tumorigenesis. We wish to understand the role of PP2A in tumor formation by SV40 and polyoma viruses by analyzing the crystal structure of the regulatory A subunit of PP2A. At beamline 7-1 at SSRL during May 16-17, 1995 we collected a 77% complete, native data set with 6.4% R sym to 3.1 w. The difference synchrotron radiation makes is dramatic: it's high intensity and narrow collimation improves spatial resolution of the spots and increases diffraction by at least 2.4w over what we can achieve in our lab.